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If you had a super powerful gamma-ray creating gun what would it be like?

Would it be similar to on sci-fi shows where they have laser guns that can pierce a hole through an enemy more effective than a bullet?

Or would it be relatively lame and have no immediate effects?

Or how about the gamma rays convert their energy into thermal energy and you explode due to the water in your body.

Would any of these happen or am I just having some super cool childish fantasies and if it is effective how hard would it be to make?

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  • $\begingroup$ For fun, this page (sandia.gov/Pulsed-Power/research_facilities/…) has a picture of a 20MeV gamma gun. Not something to carry around with you, but it would do lots of harm if you stood in front of it when it fired. $\endgroup$ – Jon Custer Feb 21 '18 at 14:54
  • $\begingroup$ what research have you done yourself? $\endgroup$ – pentane Feb 27 '18 at 1:58
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A lot depends on the energy of the gamma-ray beam as a whole and the energy of the gammas themselves. The more energetic they are, the deeper they penetrate - which means they might come out on the other side of the target without having deposited much energy and doing damage.

For low-energy 100 MeV gammas the attenuation length (the distance where 60% of them gets absorbed) in water is about 4 cm, while for 2000 MeV gammas it is more than 10 cm. Lead is about a factor of 10 shorter. So if you fired your 2000 MeV beam at a person a fair bit of energy would just pass through, while the 100 MeV beam would all deposit it in the first few centimetres.

The absorbed energy leads to electrons and x-ray photons bouncing away in all directions, further interacting with the target. In normal radiation physics this is where things would be complicated because we would try to estimate the biological effects, many of which are long-term. But if you are just pouring on a lot of energy eventual cancer risk is hardly the main problem of the target. Basically you will heat a volume of tissue (or whatever else you are hitting) with the energy of the death ray.

This is where the overall power of the beam matters: if it is just a few Watt it will just gently heat the target. If it is in the kilowatt range it will increase temperature of heavy targets by hundreds of degrees (and less for watery targets since the heating gets spread out over a much larger volume), if it is in the megawatt range we will presumably see a steam explosion if you hit somebody (the heat of vaporisation for water is 2257 J/g, so if the affected volume is about a litre you will supply that energy in 2.3 seconds with a 1 MW beam).

In the end, what is doing the damage is the total energy supply rather than it being gamma rays, although having the energy absorbed in the volume rather than on the surface might have important effects on the type of damage.

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I agree with Anders Sandburg in most of what he says, but there is a large mistake that he probably made inadvertently. In his second paragraph he should have used keV instead of MeV. Cancer patients are routinely treated with 4 to 25 MeV x-ray beams. These numbers refer to maximum photon energy as the average is quite a bit less. The depth of maximum absorbed dose in water for 6 MeV (max) photons is about 1.5 cm. At 10 cm depth the absorbed dose is about 67% of the maximum dose at 1.5 cm.

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